1. Field of the Invention
This invention relates to pressure relief devices for a pressure vessel and, in particular, to a thermally releasable alloy for use in a pressure release device in a fiber wound pressure vessel.
2. Description of the Prior Art
Pressure vessels for shipping liquids and gases under high pressure have generally been confined to metal, since metal has been recognized as the one material capable of withstanding the cyclical pressurizations and depressurizations of the vessel and to properly ventilate when the vessel is subjected to excessive temperatures.
Specifically, certain governmental agencies require that any vessel shipped in interstate commerce that contains fluids or gases under high pressure, must contain a pressure release device which will safely vent the fluids or gases in the event the vessel is subjected to excessive heat, such as might result from a fire caused by a train or truck wreck or the like.
The metal of the pressure vessel, being heat conductive, has made it possible to provide the vessel with a pressure relief valve such that when the pressure in the vessel reaches a certain value, the valve will release and permit the contents of the vessel to safely escape.
With the introduction and successful application of fiber wound pressure vessels, such as shown in U.S. Pat. Nos. 3,843,010 and 3,815,773, it is possible to manufacture pressure vessels capable of withstanding the cyclical pressurization and depressurization required by the governmental agencies with a vessel that is much lighter in weight. Heretofore, it has been impossible to obtain government agency approval for shipment in interstate commerce of the fiber wound vessels containing fluids or gases under pressure without attachment to expensive secondary electrical or pyrotechnic vent devices, because the pressure relief valves, of the type used in metal pressure vessels, would not function before the fiber wound vessel reached a degradation temperature, thereby permitting an explosive release of the fluids or gases. This was due, in large measure, to the fact that the fiber wound vessels would not conduct the heat from the fire sufficiently to build up adequate pressure within the vessel to release the pressure relief valve prior to rupture of the vessel.